Heater Blower Motor Resistor | CarsHeater Blower Motor Resistor; If none of the fan speeds work, then checking the fuse or fuses for the heating, vent and air conditioning systems is a logical first step. and certifiedHow to fix a car heater | How a Car WorksHow to fix a car heater. If your fan has several speeds, they are usually controlled by a large resistor block mounted piggy-back on the fan motor. For slow speeds the dash switch directs the current to the motor via the resistor block. If fitting a new fuse fails to solve the problem, or if the other components controlled by the fuse